Periodic Reporting for period 4 - ConFluReM (Controlling Fluid Resistances at Membranes)
Reporting period: 2021-03-01 to 2021-08-31
With respect to the prevailing challenge of fluid related resistances in membrane separation processes, the proposed research develops a rigorous methodology to control and improve mass transport through the membrane-fluid interface. Therefore “Controlling Fluid Resistances at Membranes” (ConFluReM) establishes strategic tools in fabrication, characterization, and simulation to develop new instruments to:
i) comprehend and quantify the prevalent mass transport resistances in representative membrane separation processes,
ii) synthesize and fabricate nano-, micro- and mesoscale material systems as instruments to control and overcome the limitations of concentration polarization and fouling,
iii) ultimately control and overcome the negative influence of concentration polarization and concentration polarization induced fouling and scaling.
During the project, mass transport resistances were visualized by analyzing fluid and particle movement around the membrane surface. In many cases, these resistances could be efficiently reduced by introducing targeted mixing around the membrane-fluid interface. For example, for electrically driven water desalination, printed polymer patterns on top of the membrane were shown to induce vortices that mix the laminar boundary layer and reduce its resistance. For filtration and oxygenation applications, hollow fiber membranes with built-in static mixers were produced. These mixers induce additional turbulence close to the membrane, counteract membrane fouling and enhance mass transport. Many of these advances have been tested on the process scale and enabled more efficient and sustainable water desalination, energy storage in redox flow batteries, or blood oxygenation.
Here, our research is outlined, addressing new instruments to quantify, prevent, and overcome mass transport resistances at the membrane-fluid interface. ConFluReM goes dramatically beyond common measures: it aims to introduce turbulence and better mixing at the membrane surface while minimizing energy dissipation. This is achieved through designing, describing and optimizing the nano-scale membrane surface properties, the channel topology for fluid flow, and the initiation and continuous actuation of transient gradients in the fluid channels.
Here we demonstrate our approach to the design, description and development of sterile membrane filters that emerged recently to pretreat dialysate liquids fed to a hemodialysis filtration process. Their application significantly enhances the survival rate during dialysis treatment. However, little is known about the fluid-flow coupled mass transport in such single-use membrane modules. We report a detailed analysis of the local three-dimensional flow field and its effects on i) the local permeate flux distribution identifying the active membrane area, ii) the time-dependent silica particle deposition during membrane filtration, and iii) the effect of drag force on the silica particle deposition onto the membrane. These detailed insights encourage the use of our new strategic flow imaging competences when designing new membrane module configurations.